The invention relates to a drive shaft for motor vehicles.
Pipes have been used as drive shafts for motor vehicles and it is known to produce such pipes from steel as well as aluminum materials. Further, in as far as steel pipes are installed, such steel pipes can be straight seam welded pipes.
The requirements for drive shafts are satisfactorily met with straight seam welded steel pipes, especially with regard to dynamic characteristics. However, it is disadvantageous that the steel pipe has a relatively heavy weight compared to pipes made of aluminum. One endeavors, therefore, to utilize aluminum pipes, which are considerably lighter. The weight savings for aluminum pipes is at least approximately 30% in contrast to steel pipes. In view of the tendency in the construction of motor vehicles toward saving weight in dynamically loaded parts, whereby additional component parts, such as bearings, can be more cost-effectively designed and dimensioned, the endeavor is to use aluminum. In addition, a lower vehicle weight makes a lower fuel consumption possible.
The known drive shafts consisting of aluminum are made from extruded pipe rounds. Due to the high precision generally required for drive shafts, the known aluminum pipes must be subjected to drawing for forming drive shafts, which is associated with a considerable expenditure.
As is generally known, the dynamic characteristics stand at the forefront among others for drive shafts, from which the high precision noted becomes an assumption. This precision relates to the maintenance of the outer diameter as well as the constant wall thickness of the aluminum pipe. Due to the high rotary speed of drive shafts, it is necessary to observe very narrow tolerances to guarantee a secure synchronism. In exceptional cases it may be necessary to weld balancing weight pieces at certain points on the pipe for incompletely finished drive shafts made of aluminum pipes in order to guarantee the synchronism striven for, or rather the required dynamic characteristics of the drive shaft in the sense of balancing. Besides that, the manufacture of extruded aluminum pipes with the relatively thin wall thicknesses required for drive shafts is connected with a high finishing technological expenditure.
Consequently, serious disadvantages still stand in the way of using aluminum for drive shafts, and the known extruded aluminum pipes must be classified as very costly and expensive due to the noted precision.
In addition to extruded aluminum pipes, straight seam welded pipes from aluminum alloys are also known. In German Patent Publication No. DE 41 42 325 A1, a method for the manufacture of driving gear supports from aluminum for vehicles, especially passenger cars, is described. The circumstances thus create the starting point that in the cases in which the extruded aluminum pipes to this point are processed into drive gear parts for motor vehicles, numerous shaping steps are required, which include hydraulic forming and internal high pressure shaping methods. As is described in the '325 German Patent Publication, the known extruded aluminum pipes have the inherent disadvantage that a hydraulic shaping is not possible for other prior working steps since the shaping capability of the material is depleted due to the previous working. It is also impossible to process anneal the material before the hydraulic shaping, since the material is either hardened or too soft and thus has lost its consistency.
To find a source material for the manufacture of gear drive supports made from aluminum alloys with this background notwithstanding, with which the necessary shaping steps can be conducted without problems, a method is proposed in the '325 German Patent Publication, in which straight seam welded pipes are made from a strain-hardening or heat treatable aluminum alloy as blanks.